The present invention relates to a low noise internal combustion engine for motor vehicles and particularly to a construction and arrangement so as to reduce noise resulting from the vibration of the engine main body while the engine is in operation.
Vibration of a crankshaft resulting from bending stress applied thereto with respect to an axis of revolution thereof is known to be main factor of vibration of the engine main body. Conventionally, all of such vibration of a crankshaft is transferred to and received by a cylinder block because of the construction in which a group of bosses consisting of upper boss sections and mating lower boss sections detachably mounted to the corresponding upper boss sections, respectively, to form a bearing aperture which receives the crankshaft are arranged so that the upper boss sections integrally formed with the cylinder block and arranged in a longitudinally spaced relationship along the crankshaft. With this conventional construction, even if the rigidity of the cylinder block is increased, a reduction in noise level from the engine is not as much as expected and an increase in weight of the engine is great.